1. Field of the Invention
The present invention relates to a method of generating shape data with a CAD (Computer-Aided Design) system, and a method of verifying shape data of a product designed by a CAD system.
2. Description of the Related Art
Heretofore, shape data of an automobile body have been generated as follows: A mock-up is formed of synthetic resin or clay, and the shapes of the mock-up are judged by human body designers according to their senses and organoleptic evaluations. Based on the judgment, the shapes are modified if necessary. Thereafter, the mock-up is three-dimensionally scanned by a scanning machine to generate shape data.
The above conventional process involves many steps and takes a long period of time to carry out. Furthermore, the finally produced shape data tend to suffer quality differences because of individual differences of different body designers.
Recent rapid advances in the computer technology have made it possible to construct a virtual mock-up on a CAD system, displaying images of an automobile body for design modifications. One known CAD system allows a body designer to evaluate convex and concave facets for each body section, and also permits a body designer to determine the degree of curvature of a displayed designed line according to curvature calculations and displays the calculated curvature with line segments depending on the curvature for the body designer to make design evaluations.
A surface virtually constructed on a CAD system comprises a plurality of free curved surfaces joined together. In order to produce an automobile body having smoothly blending surfaces, the CAD system is capable of verifying the joined states of the free curved surfaces in terms of shape data. Specifically, a vector tangential to a boundary line between free curved surfaces is determined, and a plain normal to the tangential vector is defined. Then, lines of intersection between the plain and the free curved surfaces are determined, and angles formed between the lines of intersection are determined for verifying the joined state of the free curved surfaces.
Based on the results of evaluations and verifications, the design is corrected, and shape data for machining dies are generated from the corrected design. Dies are then produced on the basis of the shape data, and various parts of automobile bodies are manufactured using the produced dies.
Even though the curvature is displayed for design evaluation, it is highly difficult for the body designer to judge whether requirements or conditions for producing machined dies are good or not, immediately from the magnitude of the displayed curvature.
In addition, verifying the joined state of the free curved surfaces at many verification points on a boundary line would result in a considerably long period of processing time.
Design data supplied to a CAD system do not take into account structural details of actual products, material properties of the products, and shape limitations based on the structures of dies that are used to manufacture the products, but are representative of only design aspects. If a design is to be evaluated using only design data, then the following problems arise:
Parts that are manufactured on the basis of shape data are bent, hemmed, and trimmed at their peripheral edges for the purpose of connecting them to other parts or keeping certain outer profiles. For example, FIGS. 27 and 28A-28C of the accompanying drawings show a design surface of a hood 2 generated by a body designer and cross-sectional shapes of various hemmed edges of the hood 2. FIGS. 28A-28C show cross-sectional shapes taken along lines 28Axe2x80x9428A, 28Bxe2x80x9428B, 28Cxe2x80x9428C of FIG. 27 which shows the design surface of the hood 2. The design surface shown in FIG. 27 illustrates the lines 28Axe2x80x9428A, 28Bxe2x80x9428B, 28Cxe2x80x9428C, but not the details of the cross-sectional shapes along those lines. Therefore, it is necessary to indicate the hemmed edges shown in FIGS. 28A-28C as production technique requirements, generate shape data of the hemmed edges based on the indications, and add the generated shape data to the shape data for manufacturing the hood 2.
When the design surface of the hood 2 and the hemmed edges thereof are actually formed with dies, the portions of the design surface near the hemmed edges tend to be deformed as the hemmed edges are formed.
Since the design surface of the hood 2 contains a relatively large planar area, the hood 2 which is actually manufactured will possibly be deformed due to gravity. Consequently, when dies are fabricated precisely from design data, a product actually manufactured from the dies may not have a desired design. Furthermore, structural limitations of the dies may make it difficult to manufacture a product exactly to a desired design. For these reasons, it is difficult for a body designer to perform real evaluations on a design unless the body designer considers production technique requirements for manufacturing parts.
There is an instance where, as show in FIGS. 29 and 30 of the accompanying drawings, the body designer wishes to verify an offset xcex1 and a distance xcex2 between two adjacent parts 4a, 4b with hemmed edges. In a three-dimensional space, the offset xcex1 and the distance xcex2 may not properly be visually observed depending on the direction in which the body designer sees the parts 4a, 4b, especially due to the presence of the hemmed edges. Accordingly, design surfaces including hemmed edges cannot accurately be verified unless shape data of those hemmed edges are added to the design surfaces.
FIG. 30 shows a cross-sectional shape taken along line 30xe2x80x9430 of FIG. 29. If the part 4a is a front fender for an automobile body and the part 4b is a door next to the front fender, then the offset xcex1 is a predetermined quantity for positioning a lower portion of the door inwardly of a lower portion of the front fender with respect to the automobile body, and is normally referred to as a tipping requirement. The distance xcex2 is a tolerant quantity for the gap between the front fender and the door. These quantities have to be set to predetermined values insofar as they will not impair the desired design.
It has heretofore been customary to verify the offset xcex1 and the distance xcex2 based on shape data generated in the manner described above, on either a plurality of displayed three-dimensional shapes which are viewed in different directions or a cross-sectional shape determined at certain reference points.
According to such a verifying process, however, it may not be possible for the body designer to grasp specific quantities of the offset xcex1 and the distance xcex2.Even if quantities of the offset xcex1 and the distance xcex2 can be determined at a certain cross section, the entire number of steps of the verifying process is large because many cross sections need to be calculated in order to evaluate the offset xcex1 and the distance xcex2 of the parts in their entirety.
Shape data of a hemmed edge have conventionally been generated as shown in FIGS. 31A-31E of the accompanying drawings. A given design surface 6 (see FIG. 31A) is cut at corners thereof, producing a design surface 7 (see FIG. 31B). Then, a hemmed flange 8 is set up on the edge of the design surface 7 (see FIG. 31C). A fillet 10 is then set up between the design surface 7 and the hemmed flange 8 (see FIG. 31D). Shape data of the fillet 10 can be generated as by setting an arc in contact with the design surface 7 and the hemmed flange 8 and generating the arc successively along the edge of the design surface 7. After the fillet 10 is set up, the hemmed flange 8 is deleted, thereby producing a design surface 9 having a desired hemmed edge constructed as the fillet 10 (see FIG. 31E).
The above conventional practice of generating shape data of a hemmed edge requires wasteful steps and processing time because the shape data of the hemmed flange 8, which will not be required as final shape data, have to be generated. Moreover, the generating practice itself is complex and time-consuming, and may lead to errors in generating shape data.
It is a general object of the present invention to provide a method of generating shape data of a hemmed edge around a design surface highly easily and quickly.
Another general object of the present invention is to provide a method of verifying shape data of a product highly easily and reliably by taking into account production technique requirements.
A major object of the present invention is to provide a method of verifying, highly easily and reliably, the curvature of an arbitrary curved line on a shape which is composed of shape data of a product.
Another major object of the present invention is to provide a method of verifying, highly easily and reliably, the curvature of an arbitrary curved surface on a shape which is composed of shape data of a product.
Still another major object of the present invention is to provide a method of determining easily the joined state of a plurality of shapes which are composed of shape data of a product and verifying the joined state highly easily and reliably.
Yet still another major object of the present invention is to provide a method of determining easily an offset and a distance between outer contour lines of adjacent shapes which are composed of shape data of a product and verifying the offset and the distance highly easily and reliably.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.